In operation of lathes for precision drilling of bores, a boring bar with a cutting edge mounted on an end of the bar is normally used. The boring bar, generally in the form of an elongated cylinder, is rigidly held in required position for a specific job by means of a clamping device. Desired features of a device for clamping of boring bars include a high degree of rigidity and sufficient strength to resist severe vibration forces generated in rotation of the equipment and a capability for being readily changed out as may be needed to accomplish different size cuts and to ensure that the stiffest bar possible would always be in use.
Prior art holders for boring bars have exhibited various disadvantages and limitations. Some of these holders have a complex structure and require adjustment by means such as by several set screws to obtain accurate centering. Resistance to adverse effects of vibration has also been a problem.
Prior boring bar assemblies are exemplified by U.S. Pat. No. 3,955,897, issued on May 11, 1976, to Roman et al; U.S. Pat. No. 4,619,564, issued on Oct. 28, 1986, to Jacobson, and U.S. Pat. No. 4,955,767, issued on Sep. 11, 1989, to Kaiser. The Kaiser patent shows a clamping mechanism in which a pair of two-part clamping screws have V-shaped ends that abut against a bar holder, providing, in combination with a support edge, a three-point clamping effect. However, the abutting ends of the screws are close to one another so that only a weak clamping effect is obtained.